A conventional photovoltaic module typically includes solar cells, a frame, a glass, a backboard and a junction box. A bypass diode is generally arranged inside the junction box. The bypass diode is inversely connected across a group of serially connected solar cells. The bypass diode is forward biased into conduction in a case that solar cells are shadowed or in fault, thus protecting the solar cells. To improve the conventional module, the conventional diode is replaced with a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) by some manufacturers to improve efficiency, and data acquisition and communication systems are integrated by some other manufacturers. The conventional photovoltaic module normally is simple in function, and needs an external converter to be connected with the grid or to supply power to a load. FIG. 1 shows an example of a conventional photovoltaic module.
For the disadvantage of the conventional photovoltaic modules, a direct current modular photovoltaic module and an alternating current modular photovoltaic module are developed.
FIG. 2 is a schematic diagram of a direct current modular photovoltaic module.
The direct current modular photovoltaic module includes a conventional photovoltaic module, a DC/DC power switching circuit and a controller. The direct current modular photovoltaic module outputs direct current power and can realize the maximum power point tracking (MPPT). The direct current modular photovoltaic module outputs a direct current voltage, which may be employed alone as a direct current bus, or may be connected in series to form a higher voltage direct current bus.
FIG. 3 is a schematic diagram of an alternating current modular photovoltaic module.
The alternating current modular photovoltaic module includes a conventional photovoltaic module, a DC/AC power switching circuit and a controller. The alternating current modular photovoltaic module outputs alternating current power and can be connected with the grid directly or supply power to an alternating current load directly.
Among the three photovoltaic modules described above, the first described conventional module cannot achieve power regulation. Although the other two can achieve power conversion and achieve independent MPPT, the modules can only output either an alternating current voltage or a direct current voltage. For a diversity of photovoltaic applications in the future, the above techniques lack flexibility and versatility.